A Challenging Bilateral Upper-Extremity Powered Prosthetic Fitting
Sandra Ramdial, C.P. (c) Sol Wierzba, R.T.P. (c) Isaac Kurtz, M.H.Sc. (PT) Sheila Hubbard, OT, B.Sc. (PT)
The bilateral high-level upper extremity amputee presents an enormous challenge to a clinic team.
A variety of treatment options, both prosthetic and non-prosthetic, are available. In order to manage the client effectively, it is critical that not only the physical but also that the psychosocial needs of the individual be considered. The use of sophisticated prosthetic technology to help amputees enhance their quality of life requires an interdisciplinary approach with a major emphasis on the input of the amputee.
Our objectives in the following case were to improve function and cosmesis for a young girl with TAR Syndrome.
Alicia (Picture 1. ) is a 12 year old girl with bilateral congenital upper-limb longitudinal limb-defects (phocomelia). There are a number of factors to consider:
- Limited R.O.M. in her shoulders and very weak
- Minimal hand functior limited to weak pinch between her fingers.
- Profuse sweating which caused great discomfort, and had damaged componentry in earlier prostheses.
- Alicia and her family wanted cosmesis combined with function.
Previous Prosthetic History
Alicia's first devices included powered VASI hands and passive friction wrists and elbows. The hands were switch controlled, using Otto Bock rocker switches. However, due to the considerable amounts of perspiration, the switches would corrode and seize up. In fact perspiration had to be poured out of her prostheses, as it would accumulate on the bottom of her sockets. In addition, she had difficulty positioning her finger tips to effectively operate the switches because of her weak overlapping fingers.
Force sensitive resistors (FSR's) were substituted, which improved her control, but perspiration seeped into the resistors which prevented them from working. Even after sealing the area as much as possible (using dental dam, aluminium foil duct tape and teflon film), moisture was still a problem. In addition, Alicia's hand function with these devices were limited due to the difficulty she had in positioning the friction wrists.
Current Approach to Fitting
Given the previous challenges we needed to consider an alternate control strategy. During assessment, we identified that there were two independent EMG sites on each residual limb. This allowed us to replace the FSR's and switches with Otto Bock electrodes for myoelectric control of the hands and posssibly electric wrist rotators.
However, to accommodate the need for more than one powered device, we required a more complex control strategy. Fortunately, a new programmable controller was in a developmental stage at the Bloorview MacMillan Centre and was used in this case. It consists of a microprocessor that allows the relationship between signals generated by the client and powered componentry to be defined in software. The controller allowed for easy assessment of various control strategies without the need to change componentry (Picture 2. ). After some experimentation, we devised the following control strategy:
- For wrist supination and hand opening, the posterior electrode is used (she just flexes or tucks back her little fingers),
- For wrist pronation and hand closing, the anterior electrode is used (she extends or moves her index finger forward).
- For mode selection (to switch from hand to wrist or from wrist to hand), she co-contracts or makes a fist.
Initially, problems were encountered due to a lot of co-contraction, since Alicia found it difficult to separate her signals. The solution was to use a first-come first-serve strategy in which the first muscle to contract is used, and the other signal is ignored. However, if the two signals are activated together (within a short period of time and a high amplitude), the system switches control from hand to wrist or from wrist to hand.
As an additional improvement so that Alicia does not have to think about which mode she is in, the control defaults to the hand when the rotator has not been used for a predetermined period (in this case 5 seconds was chosen).
Alicia's sockets are Trans-humeral dynamic suspension sockets or 1/2 and 1/2 sockets.
The upper half of the socket, or portion over the shoulder, is laminated in flexible silicone rubber. The lower portion of the socket is a rigid acrylic lamination that incorporates the electrodes. We were able to cut out the sockets in the area encompassing her fingers, as this area was no longer required to mount switches or resistors. The cut-out sockets were mounted in frame-style humeral shells. This modification increased ventilation, and as a result perspiration was greatly reduced.
Custom passive friction elbows were designed and manufactured at our Centre, using parts from existing products. VASI production friction external joints were modified and used in conjunction with lamination rings.
To reduce the effective weight of the prostheses, we kept the batteries as proximal as possible by housing battery cells within the elbows (Picture 3. ). Alicia is able to easily achieve humeral rotation, and forearm flexion and extension by passively positioning the elbows.
To further improve her function, hand positioning was optimized with child sized VASI electric wrist rotators. Another improvement to her prostheses was the addition of OMNI Wrists in combination with these electric wrist rotators (Picture 4. ).
Once rotated, the OMNI wrists allow Alicia to manually flex and extend the wrists in order to set her hands in the most advantageous positions.
For terminal devices, we reused the VASI 5-9 electric hands that were provided in her previous prostheses.
Alicia's motivation, and strong parental support have been instrumental in producing the positive results in this case. Alicia is very happy with the cosmesis gained by these devices and reports she feels more comfortable with her peers.
Functionally, Alicia has also gained some benefit. While wearing her arms in school, she is able to sit upright to do some pencil and paper work and keyboarding.
She is also able to grasp and place items more effectively (such as holding a pop can & hanging up her lunch bag or backpack at school), (Picture 5. ). One of Alicia's comments was that when she used her arms, she had super human power (just like "The Bionic Woman"). She is also excited that she can now take her dog out for a walk and hold the leash with the control and strength she previously lacked. (Picture 6. and Picture 7. , Alicia with her prostheses.)
Due to the limitations in existing hardware and technology, Alicia is still limited in A.D.L. independence. To enhance function, some form of elbow activation will need to be considered in the near future. We will also consider an alternate socket design which will be less restrictive of shoulder motion.
The fitting of these prostheses is not the final answer for Alicia, however, with continued problem solving, research and development and clinical trials, we are optimistic that we will have the ability to provide quality solutions for clients like Alicia, and other upper-extremity amputees in the future.
The Rehabilitation Engineering Department (electronic and mechanical services), the Ontario Rehabilitation Technology Consortium and the Powered Upper Extremity Prosthetics staff who helped make this work possible are gratefully acknowledged.
Bloorview MacMillan Centre - Toronto, Canada